The present invention relates to a telescopic shock absorber and, more particularly, to an improvement in a damping force regulation device for a double tube type teslescopic shock absorber.
Damping force required for a wheeled vehicle varies over a substantial range depending upon the running conditions of the vehicle. For example, while the vehicle runs in an urban area at relatively low speeds, a soft damping characteristic is needed in order to promote comfortable ride; while the vehicle cruises on a thruway at relatively high speeds, the damping characteristic has to be hard to insure stability of the vehicle.
A hydraulic shock absorber enabling the damping force to be controlled in accordance with the running conditions is disclosed in Japanese Patent Laid Open Publication No. 54-117486/79, for example. The disclosed prior art shock absorber includes a variable orifice arranged in a piston in parallel with a damping valve, so that the effective sectional area of the orifice may be controlled from the outside to adjust the damping resistance. This expedient is not fully acceptable, however, because hydraulic fluid is allowed to flow through the damping valve even though the orifice may be fully closed. The fluid routed through the damping valve limits the adjustable range of the damping force between the full-closed position and the full-opened position of the orifice, making it impossible to set up optimum damping characteristics throughout various operating conditions of a vehicle.